Electric propulsion combining a bank of batteries with an electric motor is an expanding sector of the workboat market. It works mainly for harbour craft and ferries that have easy access to charging points and which operate in confined areas.

Now the prospect of using electric propulsion for the lifeboats found on offshore installations and for ships’ lifeboats is being explored with two prototypes under trial. By using electric propulsion the designers hope to get better reliability and to reduce the maintenance costs.

Initially the concept of electric lifeboats is being aimed at the offshore rig and platform sector rather than for ships’ lifeboats. This is because any lifeboat with electric power will have a limited range compared with diesel powered lifeboats and in an emergency on a rig or platform there are likely to be rescue craft in close proximity. Diesel engines have been the standard as power units for lifeboats, both davit launched lifeboats and for the freefall type and it is this freefall type of lifeboat that is now the focus for electric power.

With electric propulsion there is the additional weight of the batteries that have to be fitted into the lifeboats but this can be partially balanced by the reduction in the capacity of the air bottles on board which with electric propulsion are only required to maintain the internal atmosphere and they are not required to supply air to the engine during the initial evacuation. However with electric propulsion on a freefall lifeboat particular attention has to be paid to the battery installation in order to insulate the batteries from the high G-forces that can result from the freefall into the water.

Apart from the forecast improved reliability of electric propulsion, the two companies involved in developing these craft are claiming that maintenance costs can also be reduced. Dutch lifeboat specialist Verhoef has been a pioneer in this development and the concept was developed from experience from their maintenance crews and the high cost involved with regular inspections and repairs on the traditional diesel-engines. According the Verhoef about 75% of the lifeboat inspection time is taken up with just the maintenance of the diesel engine so Verhoef claims that significant savings can be made and a higher level of reliability and safety achieved when an electric powered installation, with its minimal maintenance, is used.

With electric propulsion Verhoef suggests that the condition of the batteries and motor can be checked using established technology that can be simply plugged in to checking points on the installation. This compares with the high maintenance required for diesel-engined lifeboats which is partly due to their limited use and the fact that soot left in the engine can lead to extensive repairs and also have a negative effect on the performance and reliability of the evacuation system. With electric power Verhoef claims that there is a higher level of safety and guaranteed performance can be combined with a 50% overall cost reduction on regular inspection and maintenance.

As part of their development programme Verhoef is studying the possibility of being able to monitor the condition of the electrical equipment in the lifeboat remotely so that any problems can be detected at an early stage. In the longer term this might lead to extended periods between visit by maintenance crews with the travel to and from the rig adding a significant expense to the operation.

After a number of years spent on research and development Verhoef has successfully tested its first freefall lifeboat powered by an electric motor using the most advanced type of Li-Ion battery packs, currently available. One benefit is the higher level of comfort for the occupants with almost no noise when the motor is running. Lifeboats are required to be self-righting and another benefit is that this is much easier to achieve with electric propulsion that with a diesel where fuel and exhaust cut-outs are required leading to added complication.

Another lifeboat builder involved in the development of electrically power lifeboats is the Norwegian company Norsafe. They have been working on a similar project in cooperation with classification society DNV-GL and the Norwegian Maritime Authority and again, the aim of their project is to minimise the operation and maintenance costs associated with lifeboats. A conceptual study has been carried out with one of their GES 45 lifeboats which involved both model and full scale tests. Their prototype electric lifeboat is about to be launched and Norsafe claims that this new lifeboat will provide an environmentally friendly alternative to diesel-engined lifeboats.

The layout shows the battery container located near the stern with the electric motor ahead of it. The batteries are protected inside a water-cooled, ventilated and crash proof container. Like Verhoef, Norsafe claims a considerable number of advantages for electric power in lifeboats with a notable 90% reduction in the requirement for air bottles which is where a considerable saving in weight can be made to compensate for the increased weight of the battery system.

Norsafe also claims an estimated 95% less effort required for maintenance which should appeal to rig operators and this includes the benefits of being able to monitor and check the electrical installation from the shore to reduce the need for onboard monitoring. Norsafe claims that no parts of the system will require replacement during the 25 year design life of the system but it is not clear whether this applies to the batteries as well as the motor and propulsion system.

By Dag Pike